1. Field of the Invention
The invention relates to metal deforming and specifically to the formation of a necked and flanged metal container body. Apparatus for simultaneously necking and flanging an open end of a container body employs a die ring on the outer surface of the body interacting with a pair of separable rollers on the inside of the body.
2. Description of the Prior Art
In the art of manufacturing cylindrical metal containers, especially beverage cans, the open end or ends of a can body are flanged radially outwardly in preparation for placing a disc-like plate over the open end and seaming the plate to the flange to form a closed can. The most direct way of forming the flange is to apply a flanging die to the open end of the can body, resulting in a flange extending radially beyond the outer diameter of the cylindrical body. After application of the end plate and seaming of the end plate to the flange, the resulting seam or can chime remains radially extending outside the outer diameter of the finished can body. The radially extending chime is undesirable for at least two reasons: first, when the cans are packaged, the chimes abut and result in a substantial gap between the cylindrical walls of adjacent cans; and second, the metal disc placed over the open end must be larger in diameter than the diameter of the flanged can end opening, resulting in greater material costs than would be required if the flange were of smaller diameter.
The process of necking-in the open end of the can body provides a remedy to both of the stated disadvantages of the radially protruding chime. Such necking is commonly practiced by applying the open end of the body to a necking die, after which the necked body is applied to a flanging die, with the result being a can body that is both necked-in and flanged. This beverage can configuration is well-known and may be observed in many commercially available beverage containers. The need for the present machine arises from an economic desire to manufacture necked-in and flanged containers in a single step rather than in two steps, and correspondingly to employ only a single machine for the process instead of two machines. Furthermore, the presently employed processes for necking and flanging apply a column load to the cylindrical container body, thereby introducing a limiting factor in the minumum column strength required in the container body. If the column strength requirement could be reduced, the container wall could be made thinner with a resultant savings in material costs.
Most beverage cans are manufactured from either aluminum or steel. The well-known three-piece can is formed from a cylindrical body with independent top and bottom end closure plates, while the newer two-piece can is formed from a cup-like can body having an integral bottom end and an independent top end plate. The side wall of the two-piece body is of controlled thickness to minimize material content in accordance with functional requirements. For example, near the axial center of the cylindrical side wall, the metal is a minimum thickness, while the marginal edge of the side wall adjacent to the open end is relatively thicker to accommodate the flanging and seaming operations to which this area of the side wall will be subjected. This top edge of the side wall in aluminum cans is commonly between 0.009 and 0.006 inches, while in steel cans the thickness may be slightly greater, such as 0.012 inches. Thus, although the side wall thickness may vary at different axial locations in the can body, the thickness is predetermined within a close range at any one axial portion, and it is therefore possible to design can-handling equipment that anticipates can bodies formed with relative precision. Correspondingly, changes such as a decrease in column load requirements of a can body can be translated into realistic material savings through decrease in wall thickness in selected axial portions of the can body.
A number of machines have been proposed to perform combined necking and flanging operations, usually by a roll forming method that would have the advantage of substantially eliminating column load during these forming operations. No commercially practical apparatus is yet known for this purpose, since a number of factors other than the naked forming of the neck and flange must be considered in order to produce consistently acceptable containers. One such factor is that metal container bodies are coated on the interior surface with an inert material to prevent the beverage or other contents from acquiring flavor tones from the metal. Equally as important for commercial production is that the exterior surface is decorated or labelled, usually by a printing process applied to substantially the entire exterior cylindrical surface of the container. The interior and exterior coatings are applied prior to necking and flanging because of the ease in handling, printing, and coating the almost perfectly cylindrical side wall as compared to a side wall with a neck or flange at the open end thereof. Consequently, the necking and flanging apparatus must take account of these coatings and be relatively non-destructive to them, which is difficult to accomplish while forming the metal with the relative precision required for a consistent neck and flange configuration. A high friction spinning tool applied to the coatings creates a danger of scratching, and if forming forces are sufficiently great, the metal itself may flow and substantially disrupt the integrity of the coatings.
Other problems that commonly result from prior attempts at combined necking and flanging are that the flange may become overly brittle or crack, and neck formation may produce a reverse flow of metal, axially toward the base or opposite end of the can body, resulting in a bulge radially outward from the cylindrical side wall surface. The neck and flange are formed at the immediate edge of the side wall adjacent to the open end thereof, and the flange is therefore relatively uncontained by any portion of the side wall at the end opposite from the neck, with the result that the flange is inadequately controlled during formation of the neck and tends to wrinkle. Any of these problems lead to unacceptable containers. The causes may be the subject of speculation, but it is believed that the major causes are over-working of the metal, excessive compression of the metal with resultant metal fatigue, and inadequate metal control.